Optical testing apparatus comprising means for flowing liquids in free fall condition at constant flow rate

ABSTRACT

Improved photo-electric colorimeter possesses a flow system, wherein one part of a liquid to be measured falls at a constant flow rate defined substantially by a slit orifice for falling thereof and a weir for overflowing the remainder of the liquid, said falling liquid being transformed by a guiding means into a successive liquid film in a position between a light source and a photo-electric cell.

United States Patent Kishi Nov. 7, 1972 [54] OPTICAL TESTING APPARATUS[56] References Cited COMPRISING MEANS FOR FLOWING LIQUIDS IN FREE FALLCONDITION UNITED STATES PATENTS AT CONSTANT FLOW RATE 2,535,181 12/1950Way ..250/218 X [72] Inventor: Hirotoshi Kishi, Tokyo, Japan PrimaryExaminer-James W. Lawrence [73] AssIgnee: lwatsu Electnc Co., Ltd.,Tokyo, Assistant Examiner T N. Grigsby Japan Attorney-Robert E. Burnsand Emmanuel J. Lobato [22] Filed: Oct. 5, 1970 [21] Appl. No.: 78,112[57] ABSTRACT Improved photo-electric colorimeter possesses a flowsystem, wherein one part of a liquid to be measured [30] ForeignApphcanon Pnomy Dam falls at a constant flow rate defined substantiallyby a O 1969 apan ..44/91172 slit orifice for falling thereof and a weirfor overflowing the remainder of the liquid, said falling liquid 1.8.CI. being transformed a. means into a ucces- 1/10, 21/06 21/26 siveliquid film in a position between a light source [58] Field of Search..250/218; 356/244, 246, 207, and a ph0to e1ectric Ce".

10 Claims, 4 Drawing Figures PATENTEDunv 1 m2 SHEET 2 BF 2 MEANS FORFLOWING LIQUIDS IN FREE FALL CONDITION AT CONSTANT FLOW RATE BACKGROUNDOF THE INVENTION The present invention relates to an improved instrumentfor determining liquid properties such as transmittance, turbidimetryand concentration, particularly to an improved photo-electriccolorimeter.

There is a need for example, to control chemical processes whereby asmall but significant change in the concentration or other properties ina liquid stream may be quickly, accurately and, if necessary,continuously determined in order to allow accurate and effective controlof the process.

There are several known colorimeters with which attempts have been madeto provide continuous onstream properties information and it iswell-known that determination of the properties such as concentrationmay be obtained on Lambert Beers Law by measuring the transmittance,that is, the ratio of light intensity passing through the stream exposedto a light source against the original intensity of the light emittingfrom the light source.

In the known instrument, a sample liquid exposed to the light for themeasurement receives the light coming through the transparent wall of avessel, such as a cell in which the sample liquid is lodged, or thetransparent wall of a by-pass tube from the process system, throughwhich the sample liquid continuously flows. After passing through theopposite wall, the light remaining without absorption is sensed by aphoto-electric cell provided in a detector.

Such sample liquid exposing means against the light with propertransparency has a tendency to attract scale, dust or the like whichgradually attaches to the transparent wall during long usage thereof.The transparency of the wall thus suffers from the resultant layer ofthe scale, dust etc., and the measurement of the transmittance of theliquid is effected and results in inaccuracy.

Particularly, this tendency is disadvantageous for continuousmeasurement of fluctuation of the onstream properties.

The following attempts have been made to remove the resultant layer ofscale or the like or to prevent attachment of the layer in advance.

a. The exposing means of the sample liquid is provided with a suitablewiper which effects a cleaning operation upon the inner-surface of thewall passing through the light.

b. The exposing means comprises a plurality of vibrating platesoccupying the area of the wall through which the light passes.

c. The exposing means is provided with an oscillating means whichvibrates the wall due to an ultrasonic resonance method.

Each of the above-mentioned known means suffers from certain defects anddisadvantages as follows.

There is a need in the wiping means for a motor to drive the wiper andtherefore, more power expenditure is required. Further, there isdifficulty in sealing out the liquid from entering the transmissionthrough which the motor drives the wiper. Still the inner surface of thewall to be cleaned suffers by being scraped or scratched by the wiper.Still further, the layer attached to the inner surface of the wallexcluding the wiped area remains unwiped.

The vibrating means or oscillating means requires, for examples, aquartz crystal plate as the transparent vibrating element or oscillatingelement and further requires a driving means for oscillating theelement. The resultant instrument is complex and more expensive.

SUMMARY OF THE INVENTION Accordingly, a definite requirement exists inthe art for an improved instrument which is not associated with theaforementioned drawbacks of the prior art. Therefore, a primaryobjective of the present invention is to provide such an instrumentwhich effectively fulfills this need.

Another, more specific object of the present invention is to provide animproved colorimeter for accurately effecting on-stream determination ofthe solutions properties.

In order to implement these objects of the present invention, which willbecome more readily apparent as the description proceeds, the inventiveimproved instrument is manifested by the feature that the sample flowseparated from a stream to be measured is further divided into twoflows, one of which is effected to be in a form of a successive fall ata constant flow rate by a sample flow system, irrespective of variationin the flow rate of the separated sample, and the light coming from alight source is exposed directly to a continuous liquid film withcorresponding thickness, transformed from the sample fall by a guidingmeans provided in the sample flow system and the light passing throughthe film is sensed directly by a photo-electric detector, thereby anylayer for damaging the liquid properties, particularly transmittancethereof can be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be betterunderstood, when consideration is given to the following detaileddescription thereof, with reference to the accompanying drawingswherein;

FIG. 1 is a fragmentary-sectional view of a preferred embodiment of thepresent invention showing a sample flow system and arrangement of thephoto-electric devices,

FIG. 2 is a sectional view taken along the line lI-II in FIG. 1,

FIG. 3 is a sectional view taken along the line III-III in FIG. I, and

FIG. 4 is a diagrammatic view of the embodiment showing an opticalsystem, a circuit of the potentiometer and the successive liquid film ofthe sample flow system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Describing the drawingsand first considering in detail the exemplary embodiment of inventionphotoelectric colorimeter depicted in the figures, a flow system 1 of asample liquid to be measured, comprises a vessel 2 mounted on a housing3.

The vessel 2 is divided into an upstream section 4 and a downstreamsection 6 by a weir or a dam plate 7 which is designed to be lower thanthe vessel side walls in height.

The first upstream section 4 has an inlet 8 at its bottom wall near theside wall and a slit orifice or elongated opening 9 at the center of itsbottom, while the second downstream section 6 has an outlet 10 at itsbottom wall near the opposite side wall.

The slit orifice 9 is of a trumpet-shaped form in the transversalsection respective to its longitudinal direction and the width of thesection decreases downwardly as shown in FIG. 1.

There-is provided within the housing 3 guiding means comprising aU-shaped wire 11 extending downwardly from both longitudinal ends of theslit orifice 9. A funnel 12 is mounted in the bottom wall of the housing3 and its axis is aligned with that of the U-shaped wire 11 as well asthe slit orifice 9.

Detecting means in the nature of a photo-electric cell 13 is mountedwithin the side wall of the housing 3 which extends from the bottom wallof the first section 4 and a cylinder 14 is attached to the oppositeside wall in an arrangement where its axis is aligned with that of thephoto-electric cell 13. Within the cylinder 14 are disposed generatingmeans for generating electromagnetic radiation, and in this embodiment,the generating means comprises a light source 16, a pair of lenses l7and a replaceable filter 18 at the free end of the cylinder arranged toconvert the light emitting from the light source into a parallel ray bythe lenses l7 and then to filter the parallel ray through the filter 18.

A mirror 19 is disposed between the free end of the cylinder 14 and theU-shaped wire 11 and stands on the bottom wall of the'housing 3 in aposition where half of the filtered light rays are reflected by themirror 19 in a direction of another photo-sensitive cell 20 inserted inthe side wall adjacent to the opposite side walls.

The vertical plane formed by the U-shaped wire 11 comprises a verticalflow path and is positioned transversally to the axis extending from thelight source 16 to the photo-electric cell 13 through the lenses l4 andthe filter 18. The remainder of the filtered light rays thus passestransversally through the center of the U- shaped plane and then arriveat the photo-electric cell 13..

The inlet 8 of the vessel 2 is secured to a supply pipe 21, fluidlyconnected to a main pipe (not shown), through which a separated sampleliquid flows via an adjustable valve of the sample flow rate (not shown)into the first section 4 of the vessel 2. v

A discharge pipe 22, fluidly connected to the outlet 10 of the vessel 2,terminates at an opening of the mains pipe, and a hollow extension ofthe funnel l2 communicates with the discharge pipe 22.

A part of the sample liquid supplied to the first section 4 flowsvertically downwardly through the slit orifice 9 at a predeterminedfalling flow rate determined by the viscosity of the liquid, the heightof the weir 7 and the area or the size of the slit orifice 9.

The remainder of the sample liquid flows over the dam plate 7 into thesecond section 6 and then flows out of the second section 6 through theoutlet 10 thereof.

When the sample liquid is supplied at a greater flow rate thannecessaryto maintain the predetermined flow rate, the level of the sample liquidremaining in the first section 4 is substantially maintained at the samelevel as the height of the weir 7 since any excess liquid flows over theweir. Thusly, the flow of the liquid through the slit orifice 9 ismaintained at a constant flow rate. In other words, the falling rate isconstantly maintained irrespective of the variation in the supplyingrate, as long as an overflow condition is maintained as described above.It will be apparent owing to basic relations of fluid dynamics that thecritical falling rate depends on the parameters; the viscosity of theliquid, which is negligible in many cases, the height of the dam 7 andthe area of the slit orifice 9 in the above-mentioned condition.

The flow condition may be efiected by adjustable valve, while theadjustment of the height of the dam 7 is preferable for controlling thefalling rate.

The falling flow is guided downwardly along both extensions of theU-shaped wire 11 from the slit orifice 9 and the surface tension of thesample liquid effects the falling flow change to a continuous liquidfilm occupying the whole U-shaped plane of the guiding means 11 with acertain thickness, due to the constant falling rate. Continuously, theliquid in the form of the film gathers at the lower end of the wire 11and then falls into the opening of the funnel 12.

The gathered liquid passes through the hollow extension of the funnel l2and then is combined with the remainder of the sample liquid passingthrough the discharge pipe 22 from the outlet 10 of the second section6. The combined flow thusly returns to the main stream via the sampleflow system.

As already explained, in the sample flow system, it is most important tounderstand that the under-flow discharge of the vessel 2 is transformedinto a continuous film having a predetermined space or width and certainthickness, irrespective of the variation in the supplying rate over thatnecessary to maintain the predetermined falling flow rate.

The above-described arrangement is applied to, for example, aFisher-type photo-electric colorimeter as shown in FIG. 4, whichcomprises the flow system, optical system and the photo-sensing system.Numeral 23 denotes a circuit of the light source 16, which is adjustablefor light intensity due to operating a variable resistor 24. A circuit26 of a bridge-type potentiometer is provided and includes a pair ofidentical slide resistors 27 and 28, a galvanometer and a pair ofphotoelectric cells 13 and 20 at its terminals.

in the arrangement, the photo cell 13 senses the light passing throughthe liquid film, while another photo cell 20 also senses original lightreflected by the mirror 19 and then both cells generate signalscomprising electric currents corresponding to the intensity of the lightreceived, respectively.

For measurement, the pair of slide resistors 27 and 28 are adjusted tobe in a relationship where the indicator or the galvanometer ispositioned at zero point in other words, no current flows through thegalvanometer.

Now, suppose that resistance values set in both resistors are a at theresistor 27 and B at the opposite resistor 28, respectively,transmittance T of the liquid is identical to the ratio of a to B;

where, is intensity of the original light reflected by the mirror 19,while I is intensity of the light passing through the continuous liquidfilm 15.

If the liquid is a coloidal solution, the turbidity 1- of the solutionis determined by measuring the transmittance Tdue to the above-describedoperation and is calculated by the following equation.

where, L is a path length of the light in the liquid, that is, thethickness of the continuous liquid film.

Concentration C of a solution, particularly of a dilute solution, isdetermined by comparing transmittance T of the sample solution with Toof the reference solution, concentration Cr of which is predetermined,and is calculated by the following equation derived from Lambert BeersLaw.

where, Tr is transmittance of the reference solution and may be measuredby the colorimeter in advance.

As already explained, the successive liquid film exposed directly to thefiltered light is constantly maintained at its thickness L, so thattransmittance of the on-stream can be continuously measured or at anyinterval in the substantially same condition.

Fluctuation of the transmittance T, the resultant concentration C, theresultant turbidity -r or the like, is thus informed effectively,accurately and quickly, and this information can be applied to effectivecontrol of the on-stream properties. L

As to accuracy of the measurement, it is not decreased, even through theinventive colorimeter has been utilized for a long time, because of thenaked sample exposed directly to the light.

The inventive sample flow system may be applied to other types ofcolorimeters which are arranged with the reference liquid between themirror 19 and the photoelectric cell 20 as in the embodiment of FIG. 4.

The reference liquid may be contained in a suitable transparent cell orvessel, or may be in the same film as the sample liquid. Further, aplate having the same transmittance as the reference liquid may be usedas an alternative reference.

In the modification, the photo-electric cell 20 receives light passingthrough the reference instead of the original light. Ratio of resistancea to B is identical with that of I to IR;

Unknown concentration of the solution is determined by the followingequation.

where, 2 is absorptivity.

The instruments as described above are to be understood merely asexamples for carrying out the present invention and that variations maybe made to the instrument within the spirit and scope of the presentinvention.

It will be apparent for example that the type of photo-electric detectorused may be varied and it will also be apparent that the stream itselfmay flow into the inventive flow system without separation thereof.

The guiding means may be a pair of downwardly parallel extensions fromthe longitudinal ends of he slit I What we claim is:

1. In an instrument for determining physical properties of a liquid,such as transmittance, turbidity and concentration: means receptive of aliquid during use of the instrument for flowing the liquid along apredetermined flow path; means positioned along said flow path forreceiving a portion of the liquid flowing therealong and verticallyflowing same in a free fall condition at a substantially constant flowrate along a vertical flow path; generating means for generatingelectromagnetic radiation and directing same towards the verticallyflowing liquid; and detecting means for receiving the electromagneticradiation passing through the liquid and developing a correspondingoutput signal representative of the amount of radiation passing throughthe liquid.

2. An instrument according to claim 1; wherein said means for receivinga portion of the liquid and vertically flowing same at a substantiallyconstant flow rate includes means defining an elongated openingpositioned along a portion of said predetermined flow path for receivingtherethrough said portion of the liquid and delivering same to saidvertical flow path, and means disposed along said predetermined flowpath downstream from said elongated opening for maintaining asubstantially constant pressure head of liquid in the vicinity of saidelongated opening whereby the liquid flows vertically downwardly alongsaid vertical flow path at a substantially constant flow rate.

3. An instrument according to claim 2; wherein said means formaintaining a substantially constant pressure head of liquid comprises aweir positioned in said predetennined flow path downstream from saidelongated opening and extending transversely across said predeterminedflow path whereby any excess liquid not needed to maintain saidsubstantially constant pressure head of liquid flows over said weir.

4. An instrument according to claim 1; wherein said means for receivinga portion of the liquid comprises means defining an elongated openingpositioned along a portion of said predetermined flow path for receivingtherethrough said portion of the liquid, and guiding means cooperativewith said elongated opening for guiding the liquid flowing therethroughvertically downwardly in a continuous liquid film.

5. An instrument according to claim 4; wherein said guiding meanscomprises a hair of vertically extending wires each connected at one endto one of the longitudinal end portions of said elongated opening andbeing spaced apart from each other a distance effective to cause thevertically flowing liquid to adhere thereto due to the liquid surfacetension and form a continuous vertically flowing liquid film.

6. An instrument according to claim 5; wherein said means for receivinga portion of the liquid and vertically flowing same at a substantiallyconstant flow rate includes means disposed along said predetermined flowpath downstream from said elongated opening for maintaining asubstantially constant pressure head of liquid in the vicinity of saidelongated opening whereby the liquid flows vertically downwardly alongsaid vertical flow path at a substantially constant flow rate.

7. In an instrument for determining liquid properties such astransmittance, turbidity and concentration: means receptive of a liquidduring use of the instrument for forming a liquid flow falling downwardscomprising means defining a slit opening through which the liquid fallsdownwards and guiding means for guiding the falling liquid including twowire portions lying in a vertical plane which extends downwardly fromsaid slit opening whereby a thin continuous liquid film is formed; alight source positioned on one side of said vertical plane for emittingsuitable light; and a photoelectric detector positioned on the otherside of said vertical plane for sensing light emitted from said lightsource passing through the falling liquid film.

8. An instrument as claimed in claim 7; wherein said guiding meanscomprises a U-shaped wire extending downwardly from the longitudinalends of said slit opening.

9. In an instrument for determining liquid properties such astransmittance, turbidimetry and concentration: forming means receptiveof a liquid during use of the instrument for forming a liquid flowfalling downwards comprising a vessel divided by a dam plate into anupstream section and a downstream section, an inlet in said upstreamsection for supplying the liquid, means defining a slit opening inabottom portion of said upstream section through which one part oftheliquid falls, and an outlet in said downstream section for dischargingthe remainder of the liquid which flows over said dam plate from saidupstream section; a light source for emitting suitable light; and aphoto-electric detector for sensing light emitted from said light sourcepassing through the falling liquid.

10. An instrument as claimed in claim 9; including a U-shaped wireextending downwardly from the longitudinal ends of said slit openingeffective to form a thin continuous liquid film; and means positioningsaid light source and detector so that light emitted from said lightsource passes through the liquid film and is received by said detector.

1. In an instrument for determining physical properties of a liquid,such as transmittance, turbidity and concentration: means receptive of aliquid during use of the instrument for flowing the liquid along apredetermined flow path; means positioned along said flow path forreceiving a portion of the liquid flowing therealong and verticallyflowing same in a free fall condition at a substantially constant flowrate along a vertical flow path; generating means for generatingelectromagnetic radiation and directing same towards the verticallyflowing liquid; and detecting means for receiving the electromagneticradiation passing through the liquid and developing a correspondingoutput signal representative of the amount of radiation passing throughthe liquid.
 2. An instrument according to claim 1; wherein said meansfor receiving a portion of the liquid and vertically flowing same at asubstantially constant flow rate includes means defining an elongatedopening positioned along a portion of said predetermined flow path forreceiving therethrough said portion of the liquid and delivering same tosaid vertical flow path, and means disposed along said predeterminedflow path downstream from said elongated opening for maintaining asubstantially constant pressure head of liquid in the vicinity of saidelongated opening whereby the liquid flows vertically downwardly alongsaid vertical flow path at a substantially constant flow rate.
 3. Aninstrument according to claim 2; wherein said means for maintaining asubstantially constant pressure head of liquid comprises a weirpositioned in said predetermined flow path downstream from saidelongated opening and extending transversely across said predeterminedflow path whereby any excess liquid not needed to maintain saidsubstantially constant pressure head of liquid flows over said weir. 4.An instrument according to claim 1; wherein said means for receiving aportion of the liquid comprises means defining an elongated openingpositioned along a portion of said predetermined flow path for receivingtherethrough said portion of the liquid, and guiding means cooperativewith said elongated opening for guiding the liquid flowing therethroughvertically downwardly in a continuous liquid film.
 5. An instrumentaccording to claim 4; wherein said guiding means comprises a pair ofvertically extending wires each connected at one end to one of thelongitudinal end portions of said elongated opening and being spacedapart from each other a distance effective to cause the verticallyflowing liquid to adhere thereto due to the liquid surface tension andform a continuous vertically flowing liquid film.
 6. An instrumentaccording to claim 5; wherein said means for receiving a portion of theliquid and vertically flowing same at a substantially constant flow rateincludes means disposed along said predetermined flow path downstreamfrom said elongated opening for maintaining a substantially constantpressure head of liquid in the vicinity of said elongated openingwhereby the liquid flows vertically downwardly along said vertical flowpath at a substantially constant flow rate.
 7. In an instrument fordetermining liquid properties such as transmittance, turbidity aNdconcentration: means receptive of a liquid during use of the instrumentfor forming a liquid flow falling downwards comprising means defining aslit opening through which the liquid falls downwards and guiding meansfor guiding the falling liquid including two wire portions lying in avertical plane which extends downwardly from said slit opening whereby athin continuous liquid film is formed; a light source positioned on oneside of said vertical plane for emitting suitable light; and aphoto-electric detector positioned on the other side of said verticalplane for sensing light emitted from said light source passing throughthe falling liquid film.
 8. An instrument as claimed in claim 7; whereinsaid guiding means comprises a U-shaped wire extending downwardly fromthe longitudinal ends of said slit opening.
 9. In an instrument fordetermining liquid properties such as transmittance, turbidimetry andconcentration: forming means receptive of a liquid during use of theinstrument for forming a liquid flow falling downwards comprising avessel divided by a dam plate into an upstream section and a downstreamsection, an inlet in said upstream section for supplying the liquid,means defining a slit opening in a bottom portion of said upstreamsection through which one part of the liquid falls, and an outlet insaid downstream section for discharging the remainder of the liquidwhich flows over said dam plate from said upstream section; a lightsource for emitting suitable light; and a photo-electric detector forsensing light emitted from said light source passing through the fallingliquid.
 10. An instrument as claimed in claim 9; including a U-shapedwire extending downwardly from the longitudinal ends of said slitopening effective to form a thin continuous liquid film; and meanspositioning said light source and detector so that light emitted fromsaid light source passes through the liquid film and is received by saiddetector.